An UnknownObjectException is thrown by methods of classes and
interfaces in the java.rmi.activation package when the
ActivationID parameter to the method is determined to be
invalid. An ActivationID is invalid if it is not currently
known by the ActivationSystem. An ActivationID
is obtained by the ActivationSystem.registerObject method.
An ActivationID is also obtained during the
Activatable.register call.